isletPronunciation: /ˈʌɪlɪt/Definition of islet noun 1a small island. 2 Anatomy a portion of tissue structurally distinct from surrounding tissues. (islets)short for islets of Langerhans.Origin: mid 16th century: from Old French, diminutive of isle (see isle)islet in other Oxford dictionaries Definition of islet in the US English dictionary